| Sclerotinia sclerotiorum (Lib) de Bary - a filamentous Ascomycete fungus with a wide host range and geographical distribution, which is one of the most non-specific, omnivorous and successful plant pathogens. The aim of this study was to characterize the morphological, biochemical characters, pathogenicity and genetic diversity of S. sclerotiorum isolate populations from different geographical regions and host-plants in order to present the main differentiations among populations and isolates and provide some information on the phylogenetic taxa and breeding for resistance to sclerotinia stem rot.Two hundred and eighteen isolates of 5. sclerotiorum were isolated from three types of host plants (Brassica napus L., Daucus carota L and Helianthus annus L.) in six countries. Isolates from China, Russia and Canada were isolated from sclerotium, and those from Poland, Austria and Slovakia were subcultured from mycelia grown on PDA media.Forty-eight isolates of S. sclerotiorum were analyzed regarding to their growth rate of colony and morphological characters on the big Petri dish with PDAmedia (0 =18.5 cm). It was found that most of isolates from various regions were growing very fast. The growth rate of colony was significantly different among different populations (P<0.05). The growth rate from Hefei's population was the lowest (11.31 cm); that from Qinghai's population was the highest (16.8 cm), and the variance was low (CV = 6.10%). It indicated that isolates from Qinghai province was quite identical at the growth rate of colony.A significant difference was also presented on the morphological characteristics of various populations. Population from Hefei was distinctly different to the other populations. However, the morphological characteristics of isolates or populations from the same region were similar each other. At the population level, there were significant differences on the dry sclerotial weight (P < 0.01), fresh sclerotial weight (P < 0.01), single sclerotial weight (P < 0.001), sclerotial number (P < 0.05) and ratio between dry and fresh weight (P < 0.05) among various populations. It were found that a significant positive correlation between the growth rate and dry sclerotial weight (r = 0.30*) and three highly significant positive correlations between fresh weight and dry weight (r = 0.81 **), between fresh weight and single weight (r = 0.73***), between sclerotial number and single sclerotial weight (r = 0.60***) were found. It indicated that the number and weight of sclerotium were gradually increased with the growth of colony, but the single weight of sclerotium was decreased with more number of sclerotium within a stage of incubation.Concentrations of oxalic acid in the liquid medium were examined by HPLC and it was found that the concentration of oxalic acid was different among isolates. There was a negative correlation between oxalic acid concentration and growth rate of colony (r = -0.403), and two positive correlations between oxalic acid concentration and dry sclerotial weight (r = 0.424), between oxalic acid concentration and fresh sclerotial weight (r = 0.436) in vitro with no significant level. A significant negative correlation between concentration of oxalic acid and pH value (r = -0.517*) was found. It can explain that pH value may be a referential standard of oxalic acid concentration for initial pathogenic determinationThe disease severity index (DSI) and lesion length of nine isolates of S. sclerotiorum to 110 cultivars or lines of oilseed rape were repeatedly evaluated in two field stations (Borowo and Cezekwica). There were highly significant differences between the two stations, among isolates, among population of cultivars for the disease severity index and lesion length, and also significantstationxisolate interaction for lesion length and population×isolate interactions for DSI and lesion length, but interactions of stationxisolate for DSI were not significant. Cultivars Pomorzanin and Lisek consistently had the lowest disease severity ratings; however, most of cultivars were s...
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